This invention relates to the manufacture of coiled springs, e.g., helically coiled springs or conical coiled springs, including the production of wire for making the springs.
Reference is made herein to "rod" and "wire". These terms are used in the sense of their technical meaning in the metallurgical arts, namely, "rod" means rod formed by hot rolling, which may be drawn into wire, and "wire" means wire drawn from "rod".
The invention is especially concerned with the manufacture of springs which are cold wound. Where such springs of uniform pitch are required, they have heretofore generally been made from oil-tempered steel wire, which is wire formed by drawing hot rolled steel rod through a drawing die, and oil-tempering the resultant wire. Oil-tempering is a term of art identifying a process generally involving heating the wire to austenitizing temperatures, quenching it in oil, tempering it by heating it, and recoiling it. Reference may be made to Chapter 5, entitled Oil Tempering, of the Steel Wire Handbook published in 1969 by The Wire Association, Inc. for a detailed description of the oil tempering of wire. In the overall process of making springs from wire such as heretofore employed, after rod has been produced by hot rolling, it is cleaned with acid, coated with lime, and pulled through a drawing die to form wire, the wire being coiled, uncoiled, then fed for oil-tempering successively through a first heating means for austenitizing it, an oil bath for quenching it, and a second heating means for tempering it, then recoiled, and ultimately wound into springs. Prior to my invention disclosed in my U.S. Pat. No. 4,174,981 of making springs from oiltempered rod (as distinguished from wire), it was regarded as essential to draw the rod into wire for forming springs because the rod could not be made within the necessary limits of tolerance insofar as its gauge and roundness are concerned (it was generally "out-of-round" beyond the relatively close tolerance required for the winding of springs with uniform pitch), and also because the rod could not be made sufficiently smooth. The present inventon returns to the manufacture of springs from wire, including the production of the wire, but with improvements over the prior techniques.